How to Avoid Porosity in High Pressure Die Casting?

If you’re wondering how to avoid gas porosity during the high-pressure die-casting process, there are several things to keep in mind. These defects will be more obvious to the die-casting service provider during the design review process. However, quality manufacturers will often notice them during the machining process. When this happens, you’ll need to figure out how to solve the problem, and how much porosity is acceptable. Make sure that your die-casting service provider shares all necessary information and share the casting for you to help you determine the best way to fix the defect.

Process parameters

The effect of process parameters on the formation of high-pressure die-cast components prone to porosity. In a hot spot in the die, the pore area was determined and 20 micrographs were taken to obtain a statistical average of the pore area. Using quantitative metallographic techniques, pore area and roundness were determined. Pore roundness is defined as the perimeter divided by the area of the pore.

Various types of gas are released during the die casting process. This gas may get trapped in the mold cavity and increase the material’s porosity. The key is to keep the gas out of critical areas of the mold cavity. Using specialized modeling software can help manufacturers measure the porosity of their parts and adjust their processing parameters accordingly. These tools can also help them prevent the development of porosity.

Check for porosity

To check for porosity, the process engineer must observe the parts that have undergone the die casting process. This type of casting has high risks of leakage, as it often contains inflated bubble trails and bifilms. In addition to porosity, the engineer must check other factors such as the amount of supercooling, gating, and increased time that the parts are held in the die.

Porosity in high-pressure die casting is a defect that occurs in the metal. Although porosity is an indication of a material defect, it does not necessarily mean that the casting is not structurally sound. In some cases, porosity may be the result of air trapped between the mold and the metal. If the air is not forced out properly, the metal will solidify prematurely.

Preventing gas porosity

Gas porosity is usually a problem encountered during high pressure die casting, and it can be prevented by melting the metal in a vacuum or low-solubility gas atmosphere, like argon. Since liquids naturally contain dissolved gases, degassing involves exposing the melt to another gas, which reacts with the molten metal and forces it out of the casting. Degassing materials have multiple benefits, from the reduction of oxide formation to the improvement of the quality of the die-cast metals.

Visual inspection can identify gas porosity. It occurs when the parting surface becomes uneven, resulting in deformation and poor surface quality. In addition, the material is either missing completely or appears as a stripe with a depth that matches the metal liquid flow. Visual inspection may reveal gas porosity in the form of missing material or a thin metal sheet. Blisters can be identified by their appearance, and can also be caused by excessively high die temperatures or insufficient solidification time.

Optimum process conditions

To reduce the amount of porosity in your high-pressure die-casting parts, you must ensure that your molds are designed properly. In high-pressure die-casting, for example, it’s important that your parts have uniform wall thickness. Thinner walls are generally less porous, while thick walls are more prone to shrink porosity. Optimum process conditions will allow metal to flow into the part without creating porosity.

In addition to the design of the die, it is also important to optimize production conditions to avoid porosity. The most important design parameters are runner position, location of overflows, shape of cooling ducts, melting temperature and mold surface temperature. This study could not provide information on the optimal die temperature for complex parts. Therefore, we need to make additional research to find the optimal process conditions to avoid porosity.

Flow marks

Flow marks are lines or stripes in a die cast part. These lines and stripes are a result of a process in which liquid metal flows into the cavity, leaving behind traces that are later filled with molten metal. Flow marks are caused by a low filling pressure, low die temperature, excessive lubricant, and a small cross-section area. Increasing the die temperature, improving the cross-section area, and adjusting other casting parameters can help minimize flow marks.

The main difference between a low pouring pressure and a high pouring pressure is that the latter allows the molten metal to solidify before spreading in the die cavity. High pouring pressure, on the other hand, causes the metal to spread rapidly through the die, causing a slurry to form at the bottom of the die cavity. This makes the resulting part very hard and irregular, and it causes flow marks.

Sealing after machining

Vacuum impregnation is the most common method of sealing after machining to prevent porosity in high pressure die castings. This process seals the internal path of the porosity that breaches the casting wall. Vacuum impregnation is a cost-effective permanent solution that has no size limitation. This technique is also able to seal the smallest defect while allowing for maximum casting size.

During the machining process, the foundry staff checks each casting for defects and adjusting the spraying process. The machining process exposes areas where porosity is possible, which should be identified before die spraying begins. To avoid this, designers should foresee the possibility of porosity in castings and dimension parts with small machining allowances to avoid exposing surfaces to high temperatures during the casting cycle.